This invention relates to mechanisms for preventing particulate build-ups on external surfaces of viewing windows on military vehicles, e.g., tanks and personnel carriers.
Military vehicles commonly include armored hulls having endless ground-engagement tracks. When the vehicles are operating in muddy terrain the tracks tend to throw up considerable mud and/or water. Depending on specific conditions, the atmosphere in near proximity to the vehicle can have airborne particulates therein sufficient to present a visibility problem. Of special concern are relatively small particles that tend to remain suspended in the air for more than a second or two. Should the zone in front of a moving vehicle have a significant number of airborne particulates therein the moving vehicle can run into the airborne particles, thereby causing such particles to impinge on the vehicle window surfaces. The human driver and/or commander and/or gunner using the mud-coated window surface(s) is/are thus unable to effectively use the window(s) for viewing purposes.
The extent of the viewing problem is related, in part, to the location of the window vis a vis the direction of motion of the vehicle. Forwardly-facing window surfaces are more prone to accumulate dust or mud particles thereon than window surfaces facing to the rear or to the side.
The viewing windows can be located in the hull and/or on a gun turret carried atop the hull. In some cases the viewing windows are located on a hatch cover carried by the hull or turret. In many cases the observation windows are non-adjustable, i.e., non-movable. In other cases the observation windows are adjustable in the azimuth or elevational planes to permit an extended view of the terrain for locating, sighting or ranging enemy targets. The observation windows may be component parts of periscope devices, or component parts of vision lens systems, or component parts of television cameras, thermal imaging devices, etc.
Whatever the viewing window structure or placement on the vehicle, there is a problem in keeping the external surfaces of such window structures free of mud, snow, etc. when the vehicle is operating under adverse climatic conditions.
A common characteristic of such observation windows is their relatively small external surface area. Commonly such windows comprise vision blocks having external surface areas measuring only about four inches high and ten inches long (in a horizontal direction). Such vision blocks act in the nature of horizontal transparent slits in the armor wall structure.
The term "vision blocks" here refers to a relatively thick transparent block-like element having a relatively great thickness along the block optical axis, e.g., six inches. Such vision blocks are usually thick laminated structures having ten or more laminations to minimize destructive effects from enemy small arms fire.
Such "vision block" windows are designed to have relatively small exposed surface areas in order to present to the enemy force a target area as small as possible, consistent with their intended viewing functions. Due to the small effective surface areas of such windows the field-of-view through a given window is usually quite small or restricted. Any accumulation of dust, dirt, mud, snow, rain or sand on the window external surface can significantly interfere with viewing capability.
Some existing vehicles have motor-driven windshield wipers for selected ones of their observation windows. However, such wipers may not be practical when large numbers of vision blocks are being used, e.g., a turret having ten or more vision blocks extending around its peripheral roof area. In some cases it is difficult to get electrical power to a wiper motor at an observation window, e.g., when the window(s) is/are mounted in a movable hatch cover.
Other problems asssociated with the use of windshield wipers is their cost and their undesired bulk. When the vision block (viewing window) has a height of only about four inches the wiper blade can occupy such a large percentage of the window area as to partially obstruct the view through the window. Since the view through such windows is already limited (due to the small area sizes of such windows), any obstruction due to wiper mechanism can pose a survivability problem for vehicle personnel.
The present invention relates to low cost mechanisms for preventing particulate accumulations on the windows of military vehicles. A special object of the invention is to provide a low cost alternative to conventional windshield wipers, particularly an alternative mechanism that can be used with "small face area" windows of the "vision block" type. The invention is especially concerned with a mechanism for preventing the build-up of particulates on the external surfaces of forwardly-facing windows (i.e., surfaces that could run into airborne particulates in the vehicle's path).
The invention contemplates mechanism for creating a pressurized gas curtain in front of a vehicle window, whereby when the vehicle is moving through an atmosphere containing airborne particulates the pressurized gas curtain is effective to deflect particulates away from the window surface. The pressurized gas curtain acts as a shield or barrier between the airborne particles and the window surface.